Recently, with increased capacity and coming into widespread use of a digital record (recording, recordable or recorded) medium, increasing importance is attached to prevention of copying or inhibition of unauthorized use. That is, since digital audio data or digital video data can be duplicated free of deterioration by copying or dubbing, while computer data an be easily copied to produce the same data as the original data, unauthorized copying is made frequently.
For avoiding unauthorized copying of the digital audio or video data, there is known a standard such as a so-called serial copying management system (SCMS) or copy generation management system (CGMS). Since these systems set a copying inhibition flag on a specified portion of record data, a problem is raised that data can be extracted by dump copying which is the copying of a digital bi-level signal in its entirety.
It is also practiced to cipher the contents of a file itself in case of computer data and to permit use only by regular registered user, as disclosed in, for example, Japanese Patent laid-Open No. SHO-60-116030. This is connected to a system in which a digital record medium having the ciphered information recorded thereon is distributed as a form of information circulation and in which the user pays a fee for the information he or she needs to acquire a key to decipher the information for use. For this system, a simplified useful technique for ciphering has been a desideratum.
In view of the above-depicted status of the art, it is an object of the present invention to provide a data recording method and apparatus, a data record medium and a data reproducing method and apparatus whereby ciphering can be realized by a simplified structure, prevention of copying or unauthorized use can be achieved by a simplified configuration, deciphering is rendered difficult and relative facility or depth of ciphering can be controlled easily.